1. Field of the Invention
This invention relates to a building panel, and in particular to a composite panel of the type including a foam plastic core and metal facings.
2. Discussion of the Prior Art
Panels of the type described herein include a polyurethane foam core and metal facings, and are normally used to construct cold storage areas, for example in the food and fishery industries. Typically, the panels are approximately four feet wide and as high as an entire building, e.g. 25 to 30 feet. The thickness of the cores of the panels is determined by the amount of insulation required. Panels of this type are frequently constructed with flat side edges which abut each other. This construction provides very little strength at the joint. Also, in panels of this type, it is desirable to minimize air and water infiltration and to design the joints between panels to ensure metal to metal, and insulation to insulation contact only. Otherwise, heat or cold is conducted through the panels, or through fasteners used to connect the panels to underlying structural supports. Many prior art panels have unacceptable insulating qualities.
In general, it has not been possible or economical to construct entire buildings using insulated panels for exterior cladding. Such buildings usually include precast concrete panels or corrugated metal siding as exterior cladding. There is a great advantage in having exterior cladding which provides superior insulating qualities than traditional materials. When constructing manufacturing plants or warehouses, relatively thin insulating panels are desirable. However, the panels must have greater structural integrity than that which is available using the simple connection structure of existing insulated panels. The resulting cladding must also be aesthetically pleasing.
Fire represents another problem when using insulating panels as structural cladding. Polyurethane foam is an organic cellular foam which can be degraded by fire. A typical fire test is the ULC Fire Test Type CAN-4-S101-M82. Ordinary insulated panel systems do not survive such fire tests particularly well. The panels tend to open under high heat (approximately 1500.degree. F.) because of flexing of the metal facing sheets. Once a sheet has opened, the foam is quickly degraded by the fire. The problem could be overcome partially by screwing or otherwise externally fastening pieces of metal together. However, the screws or other fasteners would be visible and would adversely affect the appearance of the structure.
Vertical joints are normal and acceptable in insulated walls. In some cases, however, it is desirable to finish a structure with horizontal panels. Horizontal joints are not feasible using existing insulated panels, because water infiltration readily occurs in horizontal panel structures. Buildings are often under negative pressure conditions. Under positive exterior pressure, such as a driving rain storm, water may seep through the gaps between panels to degrade panel insulation, rust metal facings and fasteners and even enter the building. The water can also freeze and expand, harming the insulation, causing leakage into the building, and potentially resulting in rusting of the metal and consequently in staining of the building.
Another objectionable feature of some prior art panels is the presence of loose metal tips, edges or flanges. During shipping and handling, such loose metal pieces can be bent or torn from the foam cores of the panels causing delamination. The loose metal can also damage other panels or other objects. Since it is somewhat difficult to manipulate 30-foot long panels into interlocking engagement, delamination damage to the panels can easily occur during construction particularly when the panels are not perfectly uniform and straight. When being forced together, certain prior art panels tend to become fixed by ratcheting action. For example, edges of the metal facing may lock into the foam core of adjacent panels. Thus, the panels cannot be separated for replacement or re-use without damaging adjoining panels. Moreover, certain prior art structures require caulking in joints between panels which is an extra step in construction and requires maintenance. Also, the existence of gaps in the foam in the middle of the joints or between metal facings in certain prior art panels provides reduced insulation and potential sites for water to collect and infiltrate if caulking fails.